The present invention relates to a process and apparatus for processing and transferring an object, such as a semiconductor wafer.
Semiconductor processing equipment, such as ion-implantation equipment, sputtering equipment, etching equipment and the like, carries out a plurality of processing steps sequentially in a vacuum environment. In such equipment, it has been suggested to provide a vacuum chamber for loading semiconductor wafers to be processed. To improve process throughput, a loadlock mechanism with a gate valve is provided for separating a vacuum processing chamber from a chamber in which loading and unloading of wafer-holding cassettes are carried out.
Japanese Patent Publication No. 54-144866 (1979) describes a continuous conveyor mechanism which controls the operation of a gate valve in conveying wafer-holding cassettes into a vacuum processing chamber for sequential processing. According to this arrangement, in order to provide for a sequential processing of the cassettes by the continuous conveyor mechanism, a front and back loadlock chamber is provided at the respective front and back of the vacuum processing chamber. Further, gate valves are required at least at four locations for partitioning respective chambers in the system. Also, each of the respective chambers requires individual exhaust systems and associated complex vacuum valves and complex control mechanisms.
U.S. Pat. No. 4,836,733 discloses an arrangement for providing for a plurality of loadlock chambers for a plurality of cassettes. Semiconductor wafers are conveyed to and between respective loadlock chambers and a vacuum processing chamber. Since each loadlock chamber requires individual exhaust systems, however, an evacuation operation is required each time a cassette is placed in a respective loadlock chamber. A long process time is therefore needed for carrying out the large number of evacuation operations. This arrangement also involves a problem in that the number of exhaust systems increases the required number of machine components, with consequent lower system reliability.
Japanese Patent Publication No. 2-39523 (1990) discloses an arrangement in which three vacuum processing chambers, disposed approximately 90 degrees apart from one another, are disposed concentrically around a vacuum loadlock chamber connected thereto via respective gate valves. Wafers loaded in the vacuum loadlock chamber will be conveyed from there through the respective gate valves into a selected one of the three vacuum processing chambers. In this arrangement, it is possible for a particular wafer in the vacuum loadlock chamber to be conveyed into one of the three vacuum processing chambers disposed concentrically around the periphery thereof to be subjected to a relevant vacuum processing step. The problem is, however, that the efficiency of the system is poor because, while one wafer is being processed in a particular chamber, the remaining vacuum processing chambers are unused.
In arrangements which include conveyance systems, such as rotatable tables which carry the semiconductor wafers from one station to another, the speed at which the rotatable conveyor table can be rotated during use is limited due to the centrifugal force acting on the wafers. With high rotational velocities, the centrifugal forces can cause the semiconductor wafers to move relative to the table surface, and therefore not be precisely positioned for the next operational step. This problem of the object shifting on the turntable can be especially troublesome when the surface of the wafer or other object being carried is very smoothly finished so that the starting and sliding friction coefficient between the table surface and the object is very low.
An object of the present invention is to provide an improved semiconductor wafer processing system which includes multiple processing steps carried out in different vacuum chambers.
It is another object of the present invention to provide an object conveying system for conveying objects between work stations, while subjecting them to centrifugal force, in such a manner that the objects are not displaced relative to the conveying member due to the centrifugal forces. This object improves the speed of operation of the system by permitting more rapid conveying steps, while counteracting the centrifugal force effects in a simple and economical manner.
Certain of the above-noted and other objects of the present invention are achieved according to certain preferred embodiments of the invention by providing apparatus which includes: a plurality of vacuum processing chambers for processing the semiconductor wafers, a loadlock chamber which is evacuated by a vacuum pump, a first gate valve coupled to said loadlock chamber for loading and unloading cassettes which contains the semiconductor wafers therethrough, a plurality of second gate valves coupled to the respective loadlock chamber for shifting the semiconductor wafers from the loadlock chamber to the vacuum processing chambers therethrough, and a cassette carrier which holds the plurality of cassettes in the loadlock chamber so as to move the cassettes in front of the second gate valves.
Additional objects of the present invention are also achieved by providing a method of processing semiconductor wafers which includes the steps of: (a) conveying a plurality of cassettes which contain the semiconductor wafers to a loadlock chamber evacuated by a vacuum pump, through a first gate valve, (b) holding said a plurality of cassettes on a cassette carrier in the loadlock chamber, (c) shifting the cassettes in front of one of a plurality of second gate valves which are connected respectively to a plurality of vacuum processing chambers and (d) conveying the semiconductor wafers from the loadlock chamber to the vacuum processing chambers.
The apparatus and method of the present invention referred to above provide for an increase in the number of semiconductor wafers which can be vacuum processed for single vacuum pumping of the loadlock chamber. Further, the invention makes it possible to provide a loadlock chamber for semiconductor processing equipment which can process a plurality of wafers in vacuum continuously and automatically, featuring advantages such as a high throughput, space-saving construction, stable operation and economical manufacturing cost.
The foregoing objects with respect to counteracting centrifugal force effects so as to increase conveying speeds when using a turntable or the like which inherently imparts centrifugal forces to the object being rotated is achieved in a very simple manner by providing apparatus which includes a tilting device for tilting the conveyor surface carrying the object during movement of the conveyor surface and a control system for controlling the tilting device so as to return the conveyor surface to a desired untilted orientation when the conveying motion is stopped with the object adjacent to the next processing station. This object is also achieved by providing a method of applying the tilting movement to the conveyor surface during centrifugal force and parting movements and then applying forces to the conveyor surface to return it to a non-tilted position to accommodate the next processing or transfer to the next processing station.
The tilting arrangement for the conveyor surface to counteract the centrifugal forces on the object being conveyed is especially advantageous in currently preferred embodiments of the present invention where the system is used in conjunction with the above-described apparatus and process for processing semiconductor wafers under vacuum conditions. By placing the plurality of cassettes on a rotatable turntable at different angular positions around the table, and then applying tilting movement to the cassettes so as to counteract centrifugal forces during rapid rotation of the table between work stations, the throughput of the semiconductor wafer processing equipment is improved in a reliable and simply manner.